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In Vietnam, the presence of mycotoxins in feedstuffs intended for animal feed was first shown by Wang et al. (1995), who found high incidences of

AFB₁ in maize kernels and maize meal. In rice, the major staple food for

humans in Vietnam, Nguyen et al. (2007) found AFB₁, citrinin and

ochratoxin A in 51, 13 and 35%, respectively, of 100 rice samples. The findings of the present study also support previous studies that very high incidences (83.3% - 100%) of mycotoxins were observed in all analyzed feedstuffs and complete feeds for pigs.

High mean concentrations of AF have been detected in Indonesian maize, but the concentration of ZEA was rather low (Ali et al., 1998). In contrast, Yamashita et al. (1995) found low concentrations of AF in maize imported from the Philippines and Thailand, whereas high mean levels were

detected for ZEA. In Thailand, a similar average concentration of AFB₁ in

maize to that found in the present study was reported by Lipigorngoson et

al. (2003). Recently, Tan (2008) reported that in Southeast Asia AF was

found in a low incidence of 20%, with mean of 72 µg/kg in 180 maize samples. The incidence and mean level of ZEA was higher than that of AF and a very high amount of 5,510 µg/kg was detected in one sample. Besides

AF and ZEA, other mycotoxins such as DON, fumonisin B₁ and ochratoxin

A were also observed in maize.

The high incidence of AF in maize found in the present study probably resulted from the harvesting season and lack of equipment for drying maize. In the south of Vietnam, maize is harvested twice a year, often in the middle or at the end of the rainy season. After harvest, maize is often sun-dried or

by charcoal heated forced air-dryers. Drying is often delayed during harvest time, due to the large quantities harvested and limited equipment and techniques. In Vietnam, maize is a main component of pig feeds, and a high proportion of maize containing aflatoxins and/or ZEA can affect the performance of pigs.

The present high incidence of AF found in cassava chip might have originated during the sun-drying of the cassava roots in the field or on the road for 2 to 4 days, which is the normal drying technique in Southern Vietnam. However, ZEA was found in only one sample at detection level, which is in contrast to the data reported by Veldman et al. (1992), who found all tapioca imported from Thailand and Indonesia to be contaminated with ZEA.

The high incidences of AF and ZEA in rice bran and broken rice probably resulted during the harvesting and drying of rice. In the Mekong Delta, rice is usually harvested twice a year. After harvest it is often put to dry on the roads for three to five days before being sent to the mills, where it is sorted and directed for human or animal consumption. This practice, together with the high relative humidity, provides good conditions for mould development and formation of AF in raw rice (Trung et al., 2001). On the other hand, through rice processing, approximately 82% of the AF in raw rice will be transferred to rice bran and rice hulls, as reported by Sales and Yoshizawa (2005). In another survey, by Tan (2008), approximately 25% of rice samples were contaminated with AF. No survey of ZEA in rice bran and broken rice has been reported from Vietnam. Trung et al. (2001) could not find any strain of the main ZEA producers Fusarium graminearum and F. moniliforme in rice from the Mekong Delta. However, Chin and Tan (2006) found 17% of samples of rice and rice bran to be positive for ZEA in Asia. Recently, a high incidence of 25% in rice with a mean of 50 µg ZEA/kg was found in Southeast Asia (Tan, 2008). These results are comparable with that for rice bran and broken rice in the present study.

The present survey also revealed higher incidences of AF and ZEA in pig feeds (97.9%) compared with those in feedstuffs (90.3%). This can probably be explained by pig feeds being mainly based on maize, rice bran and cassava chip, which all have a high incidence of mycotoxins. This is also in accordance with data reported by Cespedes and Diaz (1997), who found the incidence of AF in complete feed in Colombia to be higher than in feedstuffs. A similar result was also reported by Tan (2008), who found finished feeds, comprising mainly poultry and swine feed samples, were contaminated by AF and ZEA with incidences of 22 and 37% and mean levels of 22 and 369 µg/kg, respectively.

Natural co-occurrence of AF and fumonisins in maize from tropical countries has been reported by several authors (Wang et al., 1995; Yoshizawa et al., 1996; Ali et al., 1998), but has not been reported for other feedstuffs. Yamashita et al. (1995) found only 5 and 6% of maize from the Philippines and Thailand, respectively, to be co-contaminated with AF and ZEA. A slightly higher ratio (9%) of co-occurrence of AF and ZEA was found in maize from Indonesia (Ali et al., 1998). The co-occurrence of AF and ZEA was also observed in the present study with approximately 46% of aflatoxin positive samples simultaneously contaminated with ZEA.

Although the AF and ZEA levels in the feedstuffs may be considered low in this study, they are still of concern because of the continuous high rates of inclusion of these feedstuffs in pig diets. Actually, high incidences of AF and ZEA were found in complete pig feeds, but the mean concentrations were low (less than 10 µg/kg), except for ZEA. The highest concentration of

AFB₁ was detected in complete feed for sows (39 µg/kg). This level will not

cause clear clinical effects, although over a long period of consumption it may result in chronic effects and carry-over to animal products (Lawlor and Lynch, 2001a). In contrast to AF, the highest level of ZEA 571 µg/kg was found in a complete feed for sows, and could have caused clinical effects. Pigs are the most sensitive species to ZEA, especially young gilts, and concentrations as low as 0.5 to 1 ppm may cause pseudo-oestrus and vaginal or rectal prolapse (Etienne and Dourmad, 1994, Lawlor and Lynch, 2001b).

The present result indicates a potential high exposure of pigs to both AFB₁

and ZEA, and possible chronic adverse effects on gilt and sow health.

The high incidence of AF and ZEA in feedstuffs and pig feeds in southern Vietnam found in this study highlights the need for periodic monitoring of AF, ZEA and other mycotoxins, not only in feedstuffs and animal feeds but also in food for human consumption.

5.2 Ability of local adsorbents to reduce the adverse effects of